DESCRIPTION (Applicant's Description): Marilyn Eileen Thompson received her Ph.D. in Pharmacology from the University of South Alabama in 1994 and matriculated her postdoctoral training in the laboratory of Dr. Jeffrey T. Holt at Vanderbilt University in the Department of Cell Biology. This environment provides Dr. Thompson with adequate laboratory, office space and facilities. Shared resources and equipment include liquid scintillation and gamma spectrometers, several preparative ultracentrifuges. a dark room and a cold room. Core facilities are also available for DNA sequencing, confocal laser microscopy and conventional fluorescence microscopy. Dr. Thompson has and will continue to utilize these resources as she works towards her long term career goal of becoming an established scientific investigator in cancer research. In addition, Dr. Thompson will continue to attend departmental seminars, journal clubs and weekly lab meetings as well as attending national meetings as she develops as an independent scientist. Her hypothesis is: The physiological effects of BRCA1 are determined by a dynamic equilibrium between nuclear import and export of BRCA1. Specific Aim 1: To establish that BRCA1 is actively exported from the nucleus and map the sequence that mediates this export. Transient transfection of BRCA1 DNA and microinjection of exogenous BRCA1 into cell lines will be used to characterize the export mechanism of BRCA1. Mutagenesis will be employed to map the nuclear export signal. Specific Aim 2: To elucidate whether nuclear or cytoplasmic BRCA1 functions to regulate cell proliferation and DNA repair. Stable cell lines transfected with export- defective BRCA1 will be generated in HCC1937 cells and used to determine if their rate of cell growth or ability to repair radiation-induced DNA damage is altered from that of cells with wildtype BRCA1. Specific Aim 3: To verify that BRCA1 is phosphorylated via the MAP kinase pathway, map the sites of BRCA1 phosphorylation and determine if phosphorylation of BRCA1 by MAP kinase disrupts BRCAl nuclear foci. Pharmacological manipulation of MAP kinase activity, overexpression of MAP kinase and in vitro phosphorylation assays will be used to assess the phosphorylation of BRCA1 by MAP kinase. These studies will use molecular and immunological approaches to gain fundamental knowledge of the process by which BRCA1 functions. The regulation and function of this protein are complex and these studies will provide important insight into the physiology of BRCA1 in human mammary epithelial cells.